THE ROLE OF NKX2-1 IN THE DISTAL LUNG The air sacs in the lung where oxygen and carbon dioxide are exchanged between the blood and the air are lined by alveolar epithelial cells. These cells are essential for respiratory health, and their dysfunction is associated with a range of serious diseases from birth (neonatal chronic lung disease and bronchopulmonary dysplasia) to adulthood (chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, and lung cancer). The key regulator of lung epithelial identity is NK2 homeobox 1 (NKX2-1), a transcription factor without which lungs do not even form in mammals. There are two types of alveolar epithelial cells, type 1 cells (AT1) and type 2 cells (AT2). Conventional wisdom maintains that NKX2-1 is only present in AT2 cells. However, the evidence for this belief is somewhat mixed, and we have strong evidence that NKX2-1 is also present and functional in AT1 cells. This project will use a novel technology developed in our lab to directly and definitively image the presence of Nkx2-1 in the adult mouse lung with a focus on AT1 cells. In order to then understand the actual function of Nkx2-1 in AT1 cells, we will use genetically altered mice to delete the Nkx2-1 gene in AT1 cells in the adult mouse lung and conduct detailed studies to understand how the loss of Nkx2-1 changes the AT1 cells. It is thought that the most common form of lung cancer, adenocarcinoma, comes from AT2 cells in part because lung adenocarcinoma has Nkx2-1 in it, and, as mentioned, Nkx2-1 is thought to be an AT2 marker. To determine if these Nkx2-1 tumors could actually be coming from AT1 cells, we will insert a cancer causing mutation into AT1 cells. We hypothesize that the resulting tumors will also be Nkx2-1 positive and similar in appearance to a specific type of human lung cancer called adenocarcinoma in situ. Knowing what kind of cell a cancer comes from is incredibly important in knowing how it turns into a cancer. If our hypothesis is indeed correct, this will change our understanding of where at least a portion of human lung cancers come from, thereby affecting our strategy of how to combat those cancers. This project will use the most powerful tools available in biology, including a new technology invented in our lab, to understand the role of Nkx2-1 in alveolar epithelial cells. As we transition into an era of generating specific types of cells for stem cell treatments, knowing how Nkx2-1, a ?master regulator? of lung differentiation, works will be essential in developing stem cell treatments for lung disease.